1. Field of the Invention
The present invention relates to an opaque projector, and more particularly, to an opaque real image projector for forming a real image of an object, such as a document, using the rays of light coming from a light source through a reflecting mirror, irregularly reflected by the object and arriving at an image projecting surface through a projection mirror and a projection lens.
2. Description of the Related Art
FIG. 7 shows a conventional, commonly used opaque projector of the type in which an object placed on a stage 11 made of glass or the like is directly illuminated by light sources 12. This projector also includes a projection mirror 13 for reflecting the light emanating from the object, a projection lens 14 and a casing 15.
In the opaque projector of the above-described type, the light sources 12 must be disposed at a position which ensures that the rays of light coming from the light source 12 and regularly reflected by the object and the stage 11 according to the law of reflection are not incident on the projection lens 14 through the projection mirror 13, so as to prevent deterioration in the resolution of the image caused by the regularly reflected light. Secondly, the light sources 12 have to be located outside of the angle of visibility, or field angle, of the projection lens 14. Thirdly, the light sources 12 must be located far from the stage 11 so that the stage 11 can be illuminated uniformly. However, it is practically impossible to provide a sufficiently long optical path from the viewpoint of the size of a projector, so a plurality of light sources 12 having a low luminous flux are employed to illuminate the stage 11 sideways.
To achieve more uniform illumination, the light sources 12 may be disposed farther away from the stage 11. However, this makes the resultant projector wider and taller. Also, a projector with a large number of light sources may be heavy, expensive, complicated in its structure, and is therefore inconvenient to be carried from one place to another for installation. Reversely, if the light sources 12 are located closer to the stage 11, the object will be illuminated non-uniformly.
In view of these problems, Japanese Utility Model Laid-Open No.sho 61-11148 proposes an opaque projector which is reduced in size and which is improved to eliminate the problem involving the non-uniform illumination. FIG. 8 shows this projector. In this projector, the light sources 12 are disposed at the front of the projector at a position which faces the projection mirror 13, so that the object can be illuminated by the rays of light emitting from the light sources 12 and relfected by the projection mirror 13.
Japanese Utility Model Laid-Open No.sho 61-16544 describes an opaque projector which is intended to achieve uniform illumination of an object while improving illumination efficiency. FIG. 9 shows this projector. This projector has a plurality of illumination mirrors 16 around the projection mirror 13. The illumination mirrors 16 are provided in such a manner that they expand in the upward and forward directions. The light radiating from the light sources 12 are reflected toward the stage 11 by the illumination mirrors 16 and the projection mirror 13.
However, in the opaque projector shown in FIG. 8, since the light sources 12 are disposed in opposed relation to the projection mirror 13, the rays of light radiate from the light sources 12, are reflected by the projection mirror 13, and irradiate the stage 11 and the object from the direction substantially perpendicular to them. In that case, the irradiation is reflected back by the object or the like regularly (specularly) in the direction substantially perpendicular to it owing to the law of reflection, and is incident on the projection lens 14 through the projection mirror 13, causing the resolution of the image formed to be greatly degarded, i.e., causing so-called halation.
In the case of the opaque projector shown in FIG. 9, since the rays of light radiating from the light sources 12 are all directed toward the stage 11 by the projection mirror 13 and the plurality of illumination mirrors 16 provided separately from the projection mirror 13 so as to increase the illumination efficiency, the overall illumination mirrors 16 have to have a multi-plane form so as to prevent the light regularly reflected by the object by the law of reflection from being incident on the projection mirror 13. This makes the structure of the projector complicated. Furthermore, in order to use the projection mirror 13 also as the illumination mirror, the light sources 12 have to be disposed at the two sides of the projection mirror 13 at a position which ensures that part of the illumination of the light sources 12 can be incident thereon. This, together with the complicated structure of the projector, contributes to an increased lateral dimention (the size in the lateral direction of the projection mirror 13) of the projector.